Control of adhesive flow in an inkjet printer printhead

ABSTRACT

An inkjet printer printhead has a layering of a flexible polymer tape, a patterned barrier material that is acting as an adhesive as well as ink channels, and a substrate that has a plurality of ink expulsion devices. Each of the ink propulsion devices is aligned with an orifice hole ablated in the flexible polymer tape where the ink expels and patterns the medium beyond. To keep adhesives and encapsulants required in the assembly of the inkjet printer printhead out of the critical ink channel area near the orifice holes, fluid accumulation channels are ablated into the flexible polymer tape in a strategic location between the adhesive bead and the ink channel. These accumulation channels function as both a diversion a containment point for the excess flow of adhesive.

BACKGROUND OF THE INVENTION

[0001] This invention relates to the control of the flow of an adhesivealong a substrate and more particularly to the control of the flow ofviscosity varying adhesives required in the manufacture of an inkjetprinter printhead.

[0002] Inkjet printers operate by expelling a small volume of inkthrough a plurality of small nozzles or orifices in a flexible polymertape held in proximity to a medium upon which marks or printing is to beplaced. This orificed flexible polymer tape is referred to as oriflex.The orifices are arranged in the oriflex such that the expulsion of adroplet of ink from a determined number of orifices relative to aparticular position of the medium results in the production of a portionof a desired character or image. Controlled repositioning of thesubstrate or the medium and another expulsion of ink droplets continuesthe production of more pixels of the desired character or image. Inks ofselected colors may be coupled to individual arrangements of orifices sothat selected firing of the orifices can produce a multicolored image bythe inkjet printer.

[0003] Each orifice in the oriflex is coupled to an associated smallunique ink firing chamber filled with ink and having an individuallyaddressable ink propulsion device, mounted on a substrate, and coupledto the ink. The ink is forced out of the orifice by the ink propulsiondevice, and deposited on the medium. The displaced volume of ink isreplenished from a larger ink reservoir by way of ink feed channels thatare patterned into a layer, commonly called barrier, that is interposedbetween the oriflex and the substrate.

[0004] The back surface, that which is opposite the surface facing themedia, of the oriflex includes electrically conductive traces which areterminated at the one end by large contact pads designed to interconnectwith a printer. The print cartridge is designed to be installed in aprinter so that the contact pads on the front surface of the oriflexcontact printer electrodes which provide externally generatedenergization signals to the printhead. To access these traces from thefront surface of the oriflex, holes, or vias, must be formed through thefront surface of the oriflex to expose the ends of the traces. Theexposed ends of the traces are then plated with, for example, gold toform the contact pads on the front surface, that which is facing themedia, of the oriflex.

[0005] Apertures are excised through the oriflex and are used tofacilitate bonding of the second ends of the conductive traces toelectrodes on a substrate containing ink propulsion devices. Theapertures, after bonding is complete, are filled with a bead ofencapsulating adhesive to protect any exposed portion of the traces andsubstrate. This encapsulating adhesive is referred to as encapsulant.The encapsulant is a liquid system until cross-linking takes place,creating a solid matrix when fully cured. Initially, the encapsulantdecreases in its viscosity as it is being cured, further causing it toflow before curing is complete. With no control of the flow of thisencapsulant, it is possible for the encapsulant to flow along thesubstrate, into the ink channel, and ultimately into the ink dispersionorifices. During the low viscosity state of the encapsulant, it ispossible for the adhesive to be drawn between the layer of oriflex andthe substrate, and into the ink channels formed by the barrier by acapillary force created at the exterior edge of these layers. Thisphenomenon is commonly referred to as wicking. Wicking takes place atthe oriflex to barrier interface with the encapsulant wicking along theoriflex.

[0006] Every orifice in an inkjet printer printhead has a function. Itis critical that every orifice is free from obstructions in order toeject a droplet of ink. A single orifice which does not fire an inkdroplet when it is commanded to do so will leave a portion out of aprinted character and will leave an unprinted band on the medium when asolid image is expected. This results in a poorer quality of printedmatter, highly undesirable for an inkjet printer.

[0007] Other attempts have been made to divert this flow of encapsulantaway from the ink dispersion orifices. Experiments have been performedinvolving heat cycling to control the encapsulant curing process, andadding holes in the oriflex prior to the ink channels to allow theencapsulant to escape prior to reaching the ink dispersion orifices.These experiments have met with minimal success and have, therefore,been unable to consistently control this wicking problem. Prior to thepresent invention, the wicking was noted as one of the largestcontributors to inkjet pen failure. With the invention as describedhereinafter, wicking is no longer an issue.

SUMMARY OF THE INVENTION

[0008] An inkjet printer printhead utilizes a barrier layer with an inkchannel, a first substrate disposed on a first side of the barrierlayer, and a second substrate disposed on a second side of the barrierlayer opposite the first substrate. A bonding aperture extends throughthe second substrate and the barrier layer to expose the first substratewithout entering the ink channel. An adhesive is disposed on a firstside of the second substrate opposite the barrier layer, and engulfingthe bonding aperture. At least one fluid accumulation channel isexcavated into a second side of the second substrate between the bondingaperture and the ink channel with a portion of the accumulation channelextending over the first substrate thereby reducing the flow of theadhesive from the bonding aperture into the ink channel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention can be further understood by reference tothe following description and attached drawings which illustrate thepreferred embodiment.

[0010]FIG. 1 is a perspective view of an inkjet printer print cartridgeaccording to one embodiment of the present invention.

[0011]FIG. 2 is a plan view of the top surface of the Tape AutomatedBonded (TAB) printhead assembly (hereinafter “TAB head assembly”)removed from the print cartridge of FIG. 1.

[0012]FIG. 3 is view A from FIG. 2, expanded for clarity and a betterperspective of the points of cross-sectioning for FIG. 4 and FIG. 5.

[0013]FIG. 4 is a side elevation view in a cross-section taken alongline B-B in FIG. 3 illustrating the relationship of the fluidaccumulation channels with respect to the layered components of asubstrate on a TAB head assembly.

[0014]FIG. 5 is a side elevation view in a cross-section taken alongline C-C in FIG. 3 illustrating the outermost edge of the substrate andthe wicking path of an encapsulant bead originating in a bondingaperture, flowing into the first fluid accumulation channel and wickingtoward the ink channel.

[0015]FIG. 6 is a rear view of FIG. 3, illustrating the wicking path ofthe encapsulant bead with respect to the TAB bond aperture and the fluidaccumulation channels along the bottom and exterior edges of thesubstrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] Referring to FIG. 1, reference number 101 generally indicates aninkjet printer print cartridge incorporating a printhead according toone embodiment of the present invention. The inkjet printer printcartridge 101 includes an ink reservoir 102 and a printhead 109, wherethe printhead 109 is formed using Tape Automated Bonding (TAB). Oneconventional technique is described in U.S. Pat. No. 4,917,286(Pollacek). The printhead 109 (hereinafter “TAB head assembly 109”)includes a nozzle member 108 comprising two parallel columns of offsetholes or orifices 107 formed in a flexible polymer tape 104 (hereinafter“oriflex 104”) by, for example, laser ablation. The oriflex 104 may bepurchased commercially as KAPTON tape, available from 3M Corporation.Other suitable tapes may be formed of UPILEX or its equivalent.

[0017] A back surface of the oriflex 104 includes conductive traces 207(shown from the top surface in FIG. 2) formed thereon, for example,using a conventional photolithographic etching and/or plating process.These conductive traces are terminated by large contact pads 103designed to interconnect with a printer. The print cartridge 101 isdesigned to be installed in a printer so that the contact pads 103, onthe front surface of the oriflex 104, contact printer electrodesproviding externally generated energization signals to the TAB headassembly 109.

[0018] In the various embodiments shown, the traces are formed on theback surface of the oriflex 104, opposite the surface which faces therecording medium. To access these traces from the front surface of theoriflex 104, holes, or vias are formed through the front surface of theoriflex 104 to expose the exterior trace ends 211 (FIG. 2). The exposedtrace ends are then plated with, for example, gold to form the contactpads 103 shown on the front surface of the oriflex 104.

[0019]FIG. 2 shows a front view of the TAB head assembly 109 of FIG. 1removed from the inkjet printer print cartridge 101. Bonding apertures105 and 106 extend through the oriflex 104 and are used to facilitatebonding of the interior trace ends 205 and 206 of the conductive traces207 to electrodes 410 (FIG. 4) on the substrate 210. The bondingapertures 105 and 106 are filled with a bead of encapsulating adhesive201 and 202 (hereinafter “encapsulant bead 201 and 202”) to protect anyunderlying portion of the conductive traces 207 and substrate 210 thatotherwise may be exposed through the bonding apertures 105 and 106. Itis a feature of the present invention that fluid accumulation channels208 and 209 are excavated into the oriflex 104.

[0020] Affixed to the back of the TAB head assembly 109 is a substrate210 containing a plurality of individually energizable ink propulsiondevices. Each ink propulsion device is located generally behind a singleorifice 107 and expels a droplet of ink 407 (FIG. 4) when selectivelyenergized by one or more pulses applied to one or more of the contactpads 103. The ink is supplied from the ink reservoir 102 (FIG. 1) viathe ink channel 203 which is defined in the barrier layer 204. In thepreferred embodiment, the individually energizable ink propulsiondevices are thin film resistors that are contained on a siliconsubstrate 210. Each resistor acts as an ohmic heater when selectivelyenergized, boils the ink, thereby ejecting the ink through the orifices107 and onto the medium beyond. The orifices 107 and conductive traces207 may be of any size, number, and pattern, and the various figures aredesigned to simply and clearly show the features of the invention. Therelative dimensions of the various features have been greatly adjustedfor the sake of clarity.

[0021] The cross-sectional view at line B-B of FIG. 3 is shown in FIG.4. This illustrates the substrate 210 mounted to the back of the oriflex104 and also shows one edge of the patterned barrier layer 204 formed onthe substrate 210 containing ink channels 203. The patterned barrier 204is the center layer between the substrate 210 and the oriflex 104. Shownalong the edge 417 of the barrier layer 204 are the entrances of the inkchannels 203 which receive ink from the ink reservoir 102 (FIG. 1). Theconductive traces 207 formed on the back of the oriflex 104 terminate atthe interior trace ends 206 and are bonded to the electrodes 410 locatedon the substrate 210 on the opposite side of the oriflex 104 from theconductive traces 207. The bonding aperture 105 (FIG. 3) allows accessto the ends of the conductive traces 207 and the substrate electrodes410 (FIG. 4) from the other side of the oriflex 104 to facilitatebonding.

[0022] In FIG. 4, showing a preferred embodiment of the presentinvention, fluid accumulation channels 208 are excavated or laserablated into the oriflex 104 by a series of 2 microns wide by 140microns long micro-channels separated by 2 microns wide non-ablatedspaces to a width of approximately 55 microns. An alternate embodimentis contemplated where the fluid accumulation channel 208 would beexcavated or laser ablated in the oriflex 104 by a series of 2 micronswide by 55 microns long micro-channels separated by 2 microns widenon-ablated spaces to a width of approximately 140 microns. The fluidaccumulation channel 208 patterns are included in the laser mask usedfor the ablation of the orifices 107. The spaces in the mask arenecessary to attenuate the laser beam for control of the channel depthand to avoid ablating through the oriflex 104. The ablation in thepreferred embodiment is done with an Eximer laser at a wavelength of 248nanometers, an energy of 350-400 mJ/cm2, and takes approximately 2seconds to complete. As a result of this method of ablating, the fluidaccumulation channels 208 have sloped sides 415. The finished dimensionsof the fluid accumulation channels 208 are approximately 25 microns wideand 110 microns long at the channel base 411, and approximately 55microns wide by 140 microns long at the surface of the oriflex 413. Thefluid accumulation channels 208 are spaced between the TAB bond aperture105 (FIG. 3) and the ink channel 203 (FIG. 3). The preferred embodimentutilizes the fluid accumulation channels 208 in the same orientation asthe TAB bond aperture 105 but other orientations such as angular shapes,curved shapes, etc. will perform the same function. Approximately halfof the length of the fluid accumulation channels 208 extend beyond theedge of the substrate 210 (FIG. 3). In the present invention, there arethree fluid accumulation channels 208 constructed adjacent to each comerof the substrate 210, located at the end of each of the two parallelcolumns of orifices 107 and 108 (FIG. 1). The number of fluidaccumulation channels 208 can be from one to eight and is necessitatedby the properties of the adhesive. The fluid accumulation channels 208can be constructed in a number of sizes, shapes and quantities. Thecritical criteria for the fluid accumulation channels 208 is that theycross the substrate to barrier mating edge 301.

[0023] Also shown in FIG. 4 is a side view of the oriflex 104, thebarrier layer 204, fluid accumulation channels 208, the top side bead ofencapsulant 201, the under-flow bead of encapsulant 409 which is formedwhen the encapsulant bead 201 flows through the bonding aperture 105(FIG. 1) and between the conductive traces 207 prior to cure, andadvances toward the ink channels 203. A droplet of ink 407 is shownbeing ejected from orifice 107 associated with each of the ink channels203.

[0024] The parallel lines created in the channel base 411 of the fluidaccumulation channels 208 create a capillary effect, further drawing theencapsulant from beads 201 and under-flow encapsulant bead 409 into thefluid accumulation channels 208, and keeping the encapsulant away fromthe orifices 107.

[0025] The cross-sectional view at line C-C of FIG. 3 is shown in FIG.5. FIG. 5 cuts through the oriflex 104. This view shows the side edge ofthe substrate 210, the substrate to barrier mating edge 301, and theentrance to the ink channel 203. FIG. 5 is an illustration of theunder-flow encapsulant bead 409 flowing around the comer of substrate210 at encapsulant edge 501, filling the first fluid accumulationchannel 208 and continuing the wicking path toward the next accumulationchannel.

[0026] The preferred encapsulating adhesive, GRACE, is a liquid systemuntil cross-linking takes place, creating a solid matrix when fullycured. At the onset of the curing process, the encapsulant decreases inviscosity, further causing it to flow before the curing is complete. Theamount of flow varies between encapsulants. The more potential flow, thegreater number of fluid accumulation channels 208 required to collectthe excess uncured encapsulant 501 (FIG. 5) prior to the ink channel203. The fluid accumulation channel 208 and 209 (FIG. 2) in thepreferred embodiment are ablated in all four comers of the oriflex 104as illustrated in FIG. 2.

[0027]FIG. 6 is a bottom view of the TAB head assembly of FIG. 3. Itillustrates the flow path 501 of the under-flow encapsulant bead 409.The under-flow encapsulant bead 409 wicks along the substrate edge 601toward the center of the substrate 204. Without the fluid accumulationchannels 208, the under-flow encapsulant bead 409 often flows into theink channel 203 (FIG. 5), and blocks an orifice 107 (FIG. 4). Eachorifice 107 is essential for superior print quality in the inkjetprinter print cartridge system.

[0028] In the preferred embodiment shown in FIG. 3, the addition of thefluid accumulation channels 208 to divert the encapsulant 201 that wicksalong the substrate to barrier mating edge 301 coupled with theextension of the barrier layer 204 at the substrate to barrier matingedge 301 to reduce the capillary effect previously described, theblocking of orifices 107 due to wicking encapsulant 201 has beeneffectively eliminated.

We claim:
 1. An inkjet printer printhead, comprising: a barrier layerwith an ink channel; a first substrate disposed on a first side of saidbarrier layer; and a second substrate disposed on a second side of saidbarrier layer opposite said first substrate, further comprising: abonding aperture extending through said second substrate and saidbarrier layer to expose said first substrate without entering said inkchannel; an adhesive disposed on a first side of said second substrateopposite said barrier layer and engulfing said bonding aperture; and atleast one fluid accumulation channel excavated into a second side ofsaid second substrate between said bonding aperture and said ink channelwith a portion of said accumulation channel extending over said firstsubstrate thereby reducing the flow of said adhesive from said bondingaperture to said ink channel.
 2. An inkjet printer printhead inaccordance with claim 1 wherein said substrate further comprises asubstrate edge and said barrier layer further comprises a substrate tobarrier mating edge, said substrate to barrier mating edge disposedbetween said bonding aperture and said ink channel and extending to saidsubstrate edge.
 3. An inkjet printer printhead in accordance with claim1 wherein said accumulation channel is excavated with a laser into saidsecond substrate.
 4. An inkjet printer printhead in accordance withclaim 1 wherein said accumulation channel is mechanically carved intosaid second substrate.
 5. An inkjet printer printhead in accordance withclaim 1 wherein said accumulation channel is chemically etched into saidsecond substrate.
 6. An inkjet printer printhead in accordance withclaim 2 wherein said accumulation channel crosses said substrate tobarrier mating edge.
 7. A method of manufacturing an inkjet printerprinthead comprising the steps of: excising a bonding aperture through afirst substrate; excavating at least one fluid accumulation channel in afirst side of said first substrate disposed apart from said bondingaperture; patterning a barrier layer with an ink channel; layering ontosaid first side of said first substrate said barrier layer such thatsaid ink channel is disposed between said accumulation channel and saidbonding aperture, and said second substrate onto an opposite side ofsaid barrier layer from said first substrate; and disposing an adhesiveon a second side of said first substrate to engulf said bondingaperture.
 8. A method of manufacturing an inkjet printer printhead inaccordance with claim 7 further comprising the step of excavating saidfluid accumulation channel having a portion of said fluid accumulationchannel extending over said second substrate.
 9. A method ofmanufacturing an inkjet printer printhead in accordance with claim 7further comprising the step of excavating said fluid accumulationchannel into said first substrate to a depth of less than 80 percent ofa total depth of said first substrate.
 10. A method of manufacturing aninkjet printer printhead in accordance with claim 7 further comprisingthe step of excavating said fluid accumulation channel with a width of25 to 55 microns and a length of 110 to 140 microns.
 11. A method ofmanufacturing an inkjet printer printhead in accordance with claim 7further comprising the step of excavating said fluid accumulationchannel is excavated by a laser.
 12. A method of manufacturing an inkjetprinter printhead in accordance with claim 7 further comprising the stepof excavating said fluid accumulation channel is excavated by a chemicaletch process.
 13. A method of manufacturing an inkjet printer printheadin accordance with claim 7 further comprising the step of curing saidadhesive.